dgleeson422111 wrote:
Hello All

We have a propagation issue that is confusing us. We have two 868MHz
modules on test, each capable of 500mW transmission.

We are testing to find the range of communication. We are testing them
as follows. One remains in our office while the other is taken to the
street outside. we are communicating charecter strings such as "Im at
the lamp post number 1" etc. There is somebody at each end sending
text strings in a continuous conversation. There is no protocol, error
checking or error recovery.

What we have repetadly found is that the radio in the office can
receive long after the radio in the street has stopped receiving. (The
person with the radio in the street is moving away from the office.)

The radios are the same and the power supplies to the radios are the
same. Indeed switching the radios gives the same effect.

The propagation paths between the two radios are the same in terms of
distance. However the radio signal transmitted from the office travels
through walls first before then traveling through open space. Its the
opposite for the radio in the street, firstly traveling through space
and then through the walls in the office.

We did think we had identified an interfeering source in one direction
(when moving away from the office) so we started moving in the
opposite direction. We found exactly the same effect.

Are we getting interfeerance from GSM, ISM or Paging?

As far as GSM bands go in Europe 890–915 MHz OR 1710–1785 MHz So these
shouldnt be our problem.

ISM is where we intend to operate and the greatest band occupancy
should be 10%. So we should get communication even though we would get
some interfeerance.

Paging - well this has very much gone out of fashion in Europe. But
even if it was the cause then wouldnt it be intermittant
communication. We have a constant problem.

Can anyone shed light on this phenomonon? Is it an issue of wireless
propagation that Im not familiar with or is it Interfeerance?

Best regards, and thanks for any input.

Denis
_____________________
http://www.CentronSolutions.com

What is the modulation type and data rate? Could be a delay spread
issue. Maybe the outside unit is receiving a reflected signal from the
surface of a nearby structure and is experiencing inter-symbol
interference that by chance the base unit is shielded from. This would
occur only if a high symbol rate was being used.

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P

In article m,
RFI-EMI-GUY wrote:

dgleeson422111 wrote:
Hello All

We have a propagation issue that is confusing us. We have two 868MHz
modules on test, each capable of 500mW transmission.

We are testing to find the range of communication. We are testing them
as follows. One remains in our office while the other is taken to the
street outside. we are communicating charecter strings such as "Im at
the lamp post number 1" etc. There is somebody at each end sending
text strings in a continuous conversation. There is no protocol, error
checking or error recovery.

What we have repetadly found is that the radio in the office can
receive long after the radio in the street has stopped receiving. (The
person with the radio in the street is moving away from the office.)

The radios are the same and the power supplies to the radios are the
same. Indeed switching the radios gives the same effect.

The propagation paths between the two radios are the same in terms of
distance. However the radio signal transmitted from the office travels
through walls first before then traveling through open space. Its the
opposite for the radio in the street, firstly traveling through space
and then through the walls in the office.

We did think we had identified an interfeering source in one direction
(when moving away from the office) so we started moving in the
opposite direction. We found exactly the same effect.

Are we getting interfeerance from GSM, ISM or Paging?

As far as GSM bands go in Europe 890*915 MHz OR 1710*1785 MHz So these
shouldnt be our problem.

ISM is where we intend to operate and the greatest band occupancy
should be 10%. So we should get communication even though we would get
some interfeerance.

Paging - well this has very much gone out of fashion in Europe. But
even if it was the cause then wouldnt it be intermittant
communication. We have a constant problem.

Can anyone shed light on this phenomonon? Is it an issue of wireless
propagation that Im not familiar with or is it Interfeerance?

Best regards, and thanks for any input.

Denis
_____________________
http://www.CentronSolutions.com

What is the modulation type and data rate? Could be a delay spread
issue. Maybe the outside unit is receiving a reflected signal from the
surface of a nearby structure and is experiencing inter-symbol
interference that by chance the base unit is shielded from. This would
occur only if a high symbol rate was being used.

what type of amateur radio application is this for? Or is it a
commercial application posted in this amateur radio group? just
wondering

what type of amateur radio application is this for? Or is it a
commercial application posted in this amateur radio group? just
wondering

What amateur band covers 868 MHz? Did we get a new one? I'll have to
order another transverter, I guess

Well, to get this post be on topic, does anyone know of a good source
for some SPDT coaxial relays good at 902 MHz and good for 350 Watts at
902?

Scott
N0EDV

What is the modulation type and data rate? Could be a delay spread
issue. Maybe the outside unit is receiving a reflected signal from the
surface of a nearby structure and is experiencing inter-symbol
interference that by chance the base unit is shielded from. This would
occur only if a high symbol rate was being used.



i was thinking about that...but no....

all the multi-path paths are reciprocal as well,,, so whatever the
delay spread is one way should be the same the other way.

Mark